Transgenerational effects of radiation on cancer and other disorders in mice and humans

Assessment of DNA damage in somatic and germ cells of animals living with increased radiation background and their offspring

PURPOSE

The aim of this work is to assess DNA damage in the somatic and germ cells in root voles living for a long time under conditions of an increased radiation background and to examine the of manifestation of long-term consequences in their offspring.

MATERIALS AND METHODS

Using the DNA comet assay (neutral version), we assessed the proportion of cells with DNA damage in the cells of the thyroid, bone marrow and testicular in root voles (Microtus oeconomus Pall.) that lived under conditions of increased radiation background (exposure dose rate - 0.50-20 μSv/h; Komi Republic, Russia) and in their offspring (F₁-F₃) that were reproduced in a vivarium with a normal radiation background.

RESULTS

In animals caught in a radioactively contaminated area, the level of DNA fragmentation in the thyroid gland, bone marrow and testicular remained within the range of values of control animals. The studies that we continued on the offspring of irradiated root voles that were developing in the vivarium under normal radiation background allowed us to identify an increase in the level of DNA DSBs in the thyroid gland in the F₁ generation, in the bone marrow and testicular cells in the F₂ generation. The modifying effect of urethane showed a similarity in the response of somatic cells in voles that lived for a long time in a radioactively contaminated area and in their offspring that developed with a normal radiation background. The effect of urethane was more conspicuous in thyroid cells that, than in bone marrow cells.

CONCLUSION

The data obtained on voles from the experimental site indicate adaptation to habitat conditions in a radioactively polluted environment. The provocative effect of urethane made it possible to reveal different response of organs with different proliferative activity. Long-term habitation of voles under conditions of an increased radiation background led to genome instability in their offspring.

Ionizing Radiation-Induced Epigenetic Modifications and Their Relevance to Radiation Protection

The present system of radiation protection assumes that exposure at low doses and/or low dose-rates leads to health risks linearly related to the dose. They are evaluated by a combination of epidemiological data and radiobiological models. The latter imply that radiation induces deleterious effects via genetic mutation caused by DNA damage with a linear dose-dependence. This picture is challenged by the observation of radiation-induced epigenetic effects (changes in gene expression without altering the DNA sequence) and of non-linear responses, such as non-targeted and adaptive responses, that in turn can be controlled by gene expression networks. Here, we review important aspects of the biological response to ionizing radiation in which epigenetic mechanisms are, or could be, involved, focusing on the possible implications to the low dose issue in radiation protection. We examine in particular radiation-induced cancer, non-cancer diseases and transgenerational (hereditary) effects. We conclude that more realistic models of radiation-induced cancer should include epigenetic contribution, particularly in the initiation and progression phases, while the impact on hereditary risk evaluation is expected to be low. Epigenetic effects are also relevant in the dispute about possible "beneficial" effects at low dose and/or low dose-rate exposures, including those given by the natural background radiation.